Every living thing dies at some time, plants and animals alike. When a living thing dies, its body stops working, and a body that has died does not start working again. Dead is forever. When a person dies, they no longer breathe, eat or sleep. These facts are the same for a tree, a clam and a mayfly, but one thing differs a great deal from one living thing to the next, and that is how long a life lasts, and a life can last a day or two, or thousands of years.
Start with a short life. An adult mayfly does not eat and lives only a day or two, long enough to mate and lay eggs. That is only the end of the story. Young mayflies, called naiads, live in water for months, even several years, before they become adults. Most mayflies have a life cycle of about a year, so mayflies are relatively long-lived insects.
Pacific salmon live a different kind of life. Most Pacific salmon stop eating when they return to fresh water, so they lack the energy to swim back to the ocean. After they lay their eggs, they die. Atlantic salmon do not die after spawning, so they can spawn again over several years. Riverside plants fed by dead salmon shade and cool the water and attract insects that young salmon eat.
Now consider a long life. Galapagos tortoises can live to be over a hundred years old, and one at the San Diego Zoo lived to an estimated 150, and a clam called Ming was the longest-lived single animal (not a colony) ever found, as of November 2026, and it was 507 years old when it died in 2006. The longest-lived non-colonial animal ever found is a quahog clam, Arctica islandica. The record belongs to a clam, not to a tortoise.
How do scientists know a clam's age? A quahog clam grows a new ring on its shell each year, and wide rings mean food-rich years while narrow rings mean years with less food. Ming was so old that the growth rings in its shell had become too compressed to count easily, and so scientists counted in the hinge ligament and checked the age with methods including carbon-14.
Trees keep the same kind of record. Trees typically grow one ring each year, so each ring is one year of growth, and in spring the wood cells are large with thin walls and look light, and growth slows by late summer, so the thicker-walled cells look darker. The ring pattern over a tree's whole life shows the climate it grew in, and tree-ring analysis lets scientists work out what the climate was like in the past. A dead tree can still tell its story.
The record can last long after the tree dies, and a bristlecone named Prometheus was estimated at 4,900 years old, the oldest known tree of its time, and the National Park Service calls Great Basin bristlecone pines the oldest non-clonal species on the planet, as of November 2026. Bristlecone pine wood is so dense it resists insects, fungi, rot and erosion, so some wood on the ground may be thousands of years old.
Carbon-14 tells time in another way, and it works because of what happens at death. Living things take in carbon-14 from the air. When they die they stop taking it in, and the carbon-14 in them slowly changes into other atoms. Scientists estimate how long ago a living thing died by counting the carbon-14 atoms that remain. Carbon-14 has a half-life of about 5,730 years, which means that half the atoms in a sample change into other atoms in that time.
For people, scientists count lives with averages. Life expectancy at birth in the United States was 79.0 years in 2024, up from 78.4 in 2023, as of November 2026. An average is not a promise for any one person, and it does not say how long your own life will be. It is a number that describes many lives together, and it rose between those two years. Each person's life can differ a great deal from the general figure.
After a life ends, a crew goes to work. Dead plants and animals are food for decomposers, such as bacteria, fungi and earthworms, and decomposers break dead things down into nutrients that go back into the soil, where plants can use them again. In the deep sea, microbes live off chemical energy from sulfides released as whale bones decay, and they form the base of ecosystems for as long as the food lasts. Whale carcasses in Monterey Canyon are expected to decompose in under 10 years, while whale carcasses studied off Southern California may last 50 to 100 years. Together, these processes show that death in nature is connected to continuing life, because the materials of one organism become available to others.
People and families believe different things about death, and you can ask yours what they believe. Biology can tell how long living things last and what happens to a body afterward, but it cannot answer every question people have. If a death in your life brings up feelings or questions, talk to a grown-up you trust, such as a parent, a teacher or a school counselor. They can listen, and you do not have to carry your questions alone. Asking for help is a good way to take care of yourself and of the people around you.
Words to know
- naiads: young mayflies
- spawning: laying eggs
- quahog: a hard clam
- ligament: tough body band
- expectancy: average years
